1. Field of the Invention
The present invention relates to electronic and optical switches. More specifically, the present invention relates to micro-magnetic latching switches with relaxed permanent magnet alignment requirements.
2. Background Art
Switches are typically electrically controlled two-state devices that open and close contacts to effect operation of devices in an electrical or optical circuit. Relays, for example, typically function as switches that activate or de-activate portions of electrical, optical or other devices. Relays are commonly used in many applications including telecommunications, radio frequency (RF) communications, portable electronics, consumer and industrial electronics, aerospace, and other systems. More recently, optical switches (also referred to as xe2x80x9coptical relaysxe2x80x9d or simply xe2x80x9crelaysxe2x80x9d herein) have been used to switch optical signals (such as those in optical communication systems) from one path to another.
Although the earliest relays were mechanical or solid-state devices, recent developments in micro-electro-mechanical systems (MEMS) technologies and microelectronics manufacturing have made micro-electrostatic and micro-magnetic relays possible. Such micro-magnetic relays typically include an electromagnet that energizes an armature to make or break an electrical contact. When the magnet is de-energized, a spring or other mechanical force typically restores the armature to a quiescent position. Such relays typically exhibit a number of marked disadvantages, however, in that they generally exhibit only a single stable output (i.e., the quiescent state) and they are not latching (i.e., they do not retain a constant output as power is removed from the relay). Moreover, the spring required by conventional micro-magnetic relays may degrade or break over time.
Another micro-magnetic relay is described in U.S. Pat. No. 5,847,631, (the ""631 patent) issued to Taylor et al. on Dec. 8, 1998, the entirety of which is incorporated herein by reference. The relay disclosed in this patent includes a permanent magnet and an electromagnet for generating a magnetic field that intermittently opposes the field generated by the permanent magnet. The replay must consume power in the electromagnet to maintain at least one of the output states. Moreover, the power required to generate the opposing field would be significant, thus making the relay less desirable for use in space, portable electronics, and other applications that demand low power consumption.
The basic elements of a micro-magnetic latching switch include a permanent magnet, a substrate, a coil, and a cantilever at least partially made of soft magnetic materials. In its optimal configuration, the permanent magnet produces a static magnetic field that is relatively perpendicular to the horizontal plane of the cantilever. However, the magnetic field lines produced by a permanent magnet with a typical regular shape (disk, square, etc.) are not necessarily perpendicular to a plane, especially at the edge of the magnet. Then, any horizontal component of the magnetic field due to the permanent magnet can either eliminate one of the bistable states, or greatly increase the current that is needed to switch the cantilever from one state to the other. Careful alignment of the permanent magnet relative to the cantilever so as to locate the cantilever in the right spot of the permanent magnet field (usually near the center) will permit bi-stability and minimize switching current. Nevertheless, high-volume production of the switch can become difficult and costly if the alignment error tolerance is small.
What is desired is a bi-stable, latching switch with relaxed permanent magnet alignment requirements. Such a switch should also be reliable, simple in design, low-cost and easy to manufacture, and should be useful in optical and/or electrical environments.
The micro-magnetic latching switches of the present invention can be used in a plethora of products including household and industrial appliances, consumer electronics, military hardware, medical devices and vehicles of all types, just to name a few broad categories of goods. The micro-magnetic latching switches ofthe present invention have the advantages of compactness, simplicity of fabrication, and have good performance at high frequencies, which lends them to many novel applications in many RF applications.
The present invention is directed to a micro magnetic latching device. The device, or switch, comprises a substrate having a moveable element supported thereon. The moveable element, or cantilever, has a long axis and a magnetic material. The device also has first and second magnets that produce a first magnetic field, which induces a magnetization in the magnetic material. The magnetization is characterized by a magnetization vector pointing in a direction along the long axis of the moveable element, wherein the first magnetic field is approximately perpendicular to a major central portion of the long axis. The device also has a coil that produces a second magnetic field to switch the movable element between two stable states, wherein only temporary application of the second magnetic field is required to change direction of the magnetization vector thereby causing the movable element to switch between the two stable states.
In one embodiment, the first magnet is a permanent magnet that is substantially planar and substantially parallel to the substrate.
In another embodiment, the first and the second magnets are permanent magnets that are substantially planar and substantially parallel to the substrate. In this embodiment the moveable element and the substrate are located between the first and the second magnets.
In another embodiment, the second magnet is a permalloy layer that is substantially planar and substantially parallel to the substrate.
In still another embodiment, the permalloy layer is located between the substrate and the movable element.
In yet another embodiment, the permalloy layer is located on an opposite side of the substrate from a side of the substrate that supports the movable element.
In a further embodiment, the movable element is located between the permalloy layer and the substrate, and the permanent magnet is located on an opposite side of the substrate from a side of the substrate that supports the movable element.
In another embodiment, the permanent magnet is located on an opposite side of the substrate from a side of the substrate that supports the movable
In still another embodiment, the device further comprises a second permalloy layer located on an opposite side of the substrate from a side of the substrate that supports the movable element.
In yet another embodiment, the movable element is located between the permalloy layer and the permanent magnet.
In another embodiment, the movable element is located between the substrate and the permanent magnet.
In still another embodiment, the device further comprises a second permalloy layer located between the permanent magnet and the moveable element.
In another embodiment, the device further comprises a second permalloy layer located on an outer side of the permanent magnet.
In yet another embodiment, the substrate comprises raised structures that support the moveable element.
In another embodiment, the device further comprises a pair of ground planes that sandwich the moveable element.
In still another embodiment, the permalloy layer comprises alternating discrete sections of soft magnetic material and sections of non-magnetic material, wherein the alternating sections are located along the long axis.
In another embodiment, the second permalloy layer comprises alternating discrete sections of soft magnetic material and sections of non-magnetic material, wherein the alternating sections are located along the long axis.
In yet another embodiment, the device further comprises a plurality of moveable elements supported by the substrate.
In still another embodiment, the device further comprises a plurality of moveable elements supported by the substrate.
In another embodiment, the device further comprises a plurality of moveable elements supported by the substrate, and wherein the permalloy layer comprises a plurality of laterally spaced sections, individual ones of the laterally spaced sections being in relaxed alignment with a corresponding one of the plurality of moveable elements.
In yet another embodiment, the device further comprises a plurality of moveable elements supported by the substrate, and wherein the permanent magnet comprises a plurality of laterally spaced sections, individual ones of the laterally spaced sections being aligned with a corresponding one of the plurality of moveable elements.
In still another embodiment, the device further comprises a plurality of moveable elements supported by the substrate, and wherein the permanent magnet comprises a plurality of laterally spaced first sections, individual ones of the first sections being aligned with a corresponding one of the plurality of moveable elements, and wherein the permanent magnet comprises a plurality of laterally spaced second sections, individual ones of the second sections being in relaxed alignment with a corresponding one of the plurality of moveable elements.
In another embodiment, the device further comprises a plurality of moveable elements supported by the substrate.
In yet embodiment, the device further comprises a plurality of moveable elements supported by the substrate, and wherein the permalloy layer comprises a plurality of laterally spaced sections, individual ones of the sections being in relaxed alignment with a corresponding one of the plurality of moveable elements.
In another embodiment, the device further comprising a plurality of moveable elements supported by the substrate, and wherein the permanent magnet comprises a plurality of laterally spaced sections, individual ones of the sections being in relaxed alignment with a corresponding one of the plurality of moveable elements.
In still another embodiment, the device further comprises a plurality of moveable elements supported by the substrate, and wherein the permanent magnet comprises a plurality of laterally spaced first sections, individual ones of the first sections being in relaxed alignment with a corresponding one of the plurality of moveable elements, and wherein the permanent magnet comprises a plurality of laterally spaced second sections, individual ones of the second sections being in relaxed alignment with a corresponding one of the plurality of moveable elements.
In a further embodiment, the coil comprises an xe2x80x9cS-shapedxe2x80x9d configuration. Alternatively, the coil comprises an a single coil line.
In yet another embodiment, the magnetic material comprises a permalloy. Still further, the permalloy can comprise a plurality of strips on the moveable element and aligned parallel to the long axis.
In a further embodiment, the first and second magnets are permanent magnets that are located on the substrate, and the moveable element is located between the first and second permanent magnets, each of the first and second permanent magnets having a respective long axis parallel to the long axis of the moveable element, wherein the switching between the two stable states causes the moveable element to move in a plane substantially parallel to the substrate.
In another embodiment, the coil is located on an opposite side of the moveable element from a side thereof that is supported by the substrate.
In still another embodiment, the device further comprises permalloy layers located perpendicular to the substrate and laterally spaced from the moveable element.
In yet another embodiment, the device further includes a buffer layer located between the permalloy layer and the substrate.
In another embodiment, the magnetic material comprises a permalloy having a reflective layer thereon, wherein the device functions as an optical switch when light impinges on the reflective layer such that switching the movable element between the two stable states causes the impinging light to be reflected in one of at least two different directions.
Alternatively, the magnetic material comprises a permalloy having a reflective layer thereon, and the permanent magnet having a slit located proximate to the reflective layer, wherein the device functions as an optical switch when light passed through the slit and impinges the reflective layer such that switching the movable element between the two stable states causes the impinging light to be reflected in one of at least two different directions back through the slit.
In another embodiment, the device includes a cylindrical magnet, having a center axis, that laterally encloses the moveable element such that the center axis passes through a central portion of the moveable element and is perpendicular to the substrate. The cylindrical magnet produces a first magnetic field that induces a magnetization in the magnetic material, the magnetization characterized by a vector pointing in a direction along the long axis of the moveable element, wherein the first magnetic field is approximately perpendicular to a major central portion of the long axis. In this embodiment, a coil that produces a second magnetic field to switch the movable element between two stable states, wherein only temporary application of the second magnetic field is required to change direction ofthe magnetization vector thereby causing the movable element to switch between the two stable states.
In still another embodiment, the device further comprising a first permalloy layer located on an opposite side of the substrate from a side of the substrate that supports the movable element, and a second permalloy layer located on an opposite side ofthe moveable element from a side thereof that is supported by the substrate.
These and other objects, advantages and features will become readily apparent in view of the following detailed description of the invention.
The features and advantages ofthe present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference numbers indicate identical or functionally similar elements. Additionally, the left-most digit of a reference number identifies the drawing in which the reference number first appears.
FIGS. 1A and 1B are side and top views, respectively, of an exemplary embodiment of a switch.
FIG. 2 illustrates the principle by which bi-stability is produced.
FIG. 3. illustrates the boundary conditions on the magnetic field (H) at a boundary between two materials with different permeability (m1 greater than  greater than m2).
FIG. 4 shows the computer simulation of magnetic flux distributions, according to the present invention.
FIGS. 5A-C show extracted horizontal components (Bx) of the magnetic flux in FIG. 4.
FIGS.6A and 6B show a top view and a side view, respectively, of a micro-magnetic latching switch 600 with relaxed permanent magnet alignment according to an aspect of the present invention.
FIGS. 7 and 8 show further embodiments of the micro-magnetic latching switch according to the present invention.
FIGS. 9A and 9B show a top view and a side view, respectively, of a micro-magnetic latching switch with additional features of the present invention.
FIG. 10 shows micro-magnetic latching switch with a buffer layer according to the present invention.
FIG. 11 shows a micro-magnetic latching switch with a permalloy placed under the thinned substrate according to the present invention.
FIGS. 12 and 17 show a one-end-fixed (or spring board) type micro-magnetic latching switch according to the present invention.
FIGS. 13A and 13B show a top view and side view, respectively, of a micro-magnetic latching switch 1300 with two permanent magnets according to the present invention.
FIG. 13C shows an embodiment with a permanent magnet and a multi-sectional soft magnetic layer which form the magnetic dipole, according to the present invention.
FIG. 13D shows an embodiment with two high-permeability magnetic layers and two permanent magnets according to the present invention.
FIGS. 14A-C shows simulation results confirming the usefulness of the magnetic dipoles in producing the uniform magnetic fields according to the present invention.
FIGS. 15A and 15B show a top view and a side view, respectively, of another micro-magnetic latching switch 1500 according to the present invention.
FIG. 16 is a side view of a different embodiment of a single-pole double-throw (SPDT) micro-magnetic latching switch with an xe2x80x9cS-shapexe2x80x9d coil according to the present invention.
FIGS. 18A-D show an embodiment that incorporates transmission lines suitable for transmitting radio frequency (RF) signals according to the present invention.
FIGS. 19A-D show another embodiment that incorporates transmission lines suitable for transmitting radio frequency (RF) signals according to the present invention.
FIGS. 20-29 show various micro-magnetic latching switch array embodiments according to the present invention.
FIGS. 30A and 30B show a top view and an end view, respectively, of yet another embodiment of the micro-magnetic latching switch according to the present invention, but in this case the cantilever moves sideways instead of up and down.
FIG. 31 shows another embodiment ofthe micro-magnetic latching switch according to the present invention.
FIGS. 32A and 32B show a top view and a side view, respectively, of an embodiment to integrate the micro-magnetic latching switch with other active/passive semiconductor devices and circuits, together with the permanent magnets according to the present invention.
FIGS. 33-35 show yet another method to produce RF MEMS micro-magnetic latching switches using a CPW architecture according to the present invention.
FIG. 34 shows a method to relax alignment tolerance of the CPW switch of FIG. 33 according to the present invention.
FIG. 35 shows a planar dielectric layer used to separate the top conductor from the underlying ground plane according to the present invention.
FIGS. 36A and 36B show a top view and side view, respectively, of an optical switch with a permanent magnet located on the bottom of the substrate according to the present invention.
FIGS. 37A-D show another embodiment of an optical switch, which includes a top permanent magnet according to the present invention.
FIGS. 38A-B show still another embodiment of an optical switch according to the present invention.